Hydrocarbyl sulfonate salts are very effective surfactants and can be used for example in dishwashing detergent or laundry detergents. The C.sub.10-20 aliphatic sulfonates in which the sulfonate group is on an internal carbon atom are particularly effective. Such compositions can be made by oxidizing an internal mercaptan with an oxidizing agent such as nitric acid, oxygen, hydrogen peroxide and the like. One problem with these processes is that the oxidation can produce a substantial portion of byproducts that are insoluble in aqueous base and soluble in aliphatic hydrocarbons such as pentane. These by-products are referred to as "free-oil" and include hydrocarbyl disulfides, thioesters and the like. This represents a substantial waste of starting materials and also complicates the process by requiring purification to remove the large amount of free-oil. Thus, a need exists for a process capable of oxidizing hydrocarbyl mercaptans to the corresponding sulfonic acid or salt in high yield and with minimal coproduction of free-oil.